A light unit in a car conventionally consists of an incandescent lamp, more recently a HID lamp. With the development of high power LEDs, it has become possible to design such light unit, for instance a head light, a tail light, a brake light, as a multi LED source. The present invention relates particularly to the headlight unit of a vehicle, and the invention will hereinafter specifically be explained for this application, but it is noted that the gist of the present invention is more generally applicable to any multi LED source.
The vehicle will be provided with a central controller, which decides whether the headlight as a whole should be switched off or on. For generating the LED current, the vehicle is further provided with a driver device.
In principle, it is possible that all LEDs are controlled simultaneously, for instance by being connected in parallel and/or in series. However, it is desirable that each LED can be controlled individually, among other things in order to implement different lighting functionalities (high beam, low beam, corner beam), and in order to be able to detect failure of individual LEDs. This individual controllability can be implemented by having individual LED drivers associated with the individual LEDs, each LED driver being controlled by the central controller, but this would require a plurality of LED drivers, which is costly, as well as a plurality of wiring connections between the central controller and the individual LED drivers. Alternatively, in the more cost-efficient design of one common LED driver, the individual controllability can also be implemented but would require a driver having a plurality of outputs and, again, a plurality of wiring connections between the individual driver outputs and the individual LED drivers.